In semiconductor fabrication, a chemical mechanical polishing (CMP) technique is usually used for removing excess materials formed on a semiconductor substrate and for global planarization of layers formed on the semiconductor substrate. In a CMP process, a slurry is used for both chemical and mechanical polishing, which includes chemicals and abrasive particles. Typically, the slurry is provided by a slurry dispersion system (SDS) and applied directly onto a wafer surface to be polished. The quality of the slurry affects the performance of the CMP process, such as process defects and a removal rate. If the quality of the slurry is found abnormal, the slurry dispersion system may be adjusted or stopped in order to avoid causing damages to the wafer surface in the CMP process.
Conventionally, the quality of the slurry stored in the slurry dispersion system is analyzed by an off-line monitor, but not in real time. In other words, the abnormality of the slurry cannot be detected in time, and may cause damages to the wafer surface during the CMP process before being detected by the off-line monitor, thus resulting in performance degradation of the CMP process.